Distribution, burden, and impact of acute gastroenteritis in Dominica, 2009-2010.

Acute gastroenteritis (AGE) is an important public-health issue in Dominica. To determine the burden of AGE in Dominica, a retrospective, cross-sectional population survey was conducted in March-April 2009 and October 2010 (low- and-high-AGE seasons) and a laboratory survey from April 2009 to March 2010. The overall monthly prevalence of self-reported AGE was 8.6 % (95% CI 7.0-10.6); the incidence rate was 1.1 episodes/person-year and 79,157.1 episodes of AGE for the total population/year. Monthly prevalence of AGE was the highest in the 1-4 year(s) age-group (25.0%), higher in females (10.8%) and also varied by health district, with the highest monthly prevalence of AGE being reported in the Portsmouth district (13.1%). This difference in gender and across the health region was statistically significant. The estimated underreporting of syndromic AGE to the Ministry of Health was 83.3%. Furthermore, for every reported laboratory-confirmed case of AGE and foodbome disease (FBD), there was an estimated underreporting factor of 280. Overall, 47% of AGE specimens tested were positive for FBD pathogens. The predominant pathogens isolated were norovirus, followed by Giardia, Salmonella, and Shigella. The total annual estimated cost of AGE was US$ 1,371,852.92, and the total cost per capita due to AGE was US$ 19.06, indicating an economic burden of AGE-related illness on a small island of Dominica.


INTRODUCTION
The Commonwealth of Dominica, situated between the two French Islands of Martinique and Guadeloupe, has a land area of 298 square miles and a total population of 71,293 (1). It is divided into 10 parishes and 7 health districts, with the most densely-populated parish being St. Georges; St. David parish is mostly rural. Primary healthcare services are delivered through facilities throughout the island via its seven health districts, each with a peripheral network of clinics and health centres/clinics. The Health Information Unit (HIU) is the disease surveillance unit for the Ministry of Health (2).

Distribution, Burden, and Impact of Acute Gastroenteritis in Dominica, 2009-2010
were reported in 2006 and 2007 respectively (6). Data are collected from all government health centres and selected sentinel sites. Over the last five years, Dominica has had three outbreaks of AGE. Norovirus was identified in the 2006 and 2010 AGE outbreaks. In 2008, rotavirus was identified as the aetiologic pathogen (6).
It is well-known that reported AGE represents only a small fraction of the total AGE in the community. Thus, to obtain a comprehensive picture of the distribution and burden of AGE and foodborne diseases in Dominica, the Ministry of Health, in collaboration with Caribbean Epidemiology Centre (CAREC), Pan American Health Organization (PAHO), and Ross University (RUSM), conducted a burden of illness study in Dominica during 2009Dominica during -2010. Additional technical and financial assistance was also provided by the Public Health Agency of Canada (PHAC) and the Caribbean Eco-Health Programme (CEHP). This study was part of the Caribbean Burden of Illness Study being conducted in seven other countries. The result of this study will be used in advocating for resources to improve AGE and FBD surveillance and in designing the appropriate intervention measures.

Population survey
A retrospective, cross-sectional population survey was conducted in 2 phases in all 7 health districts, using the household list maintained by the Central Statistical Office as the sampling frame. The first phase was conducted in 22 March-4 April 2009 (low-AGE season) and 17-31 October 2010 (high-AGE season). The high-and low-AGE seasons were designated based on the average 5-year syndromic AGE surveillance data. In the selected households, the individuals were interviewed on the day before the next birthday. Residents of Dominica, aged higher than 1 year, were included while persons of less than 1 year of age, those not living in Dominica at the time of the survey, prisoners, mentallydisabled persons, and those who did not consent or were unwilling to participate were excluded.

Sample-size
A sample-size of 1,204 was calculated using Epi Info (version 3.5.3) based on a population of 71,008, an expected prevalence of AGE of 15%, allowable error of 2%, and 95% confidence interval. This number was rounded to 1,210; and so, 605 interviews were conducted in each study period.

Data collection, validation, and security
The survey questionnaire was administered during face-to-face interviews by trained student nurses and community health nurses in Phase I and Phase II respectively. Verification of the interviews was done by telephone calls to 10 randomly-selected households in each phase. Respondents were asked if they had experienced any symptoms of diarrhoea in the past 4 weeks, with the case definition of diarrhoea being three episodes of loose stools (taking the shape of the container) in 24 hours. Additional questions were asked about sociodemographic factors, behavioural factors, secondary symptoms, whether cases sought medical care in public or private facilities, the use and type of medications, number of missed school and/or work days, and whether hospitalization was required.

Ethical approval
The study was approved by the National Human Research Ethics Committee of Dominica. An oath of confidentiality was also obtained from each interviewer to conduct the population survey. All data collected were kept confidential. The participants were identified by code and not by name on the questionnaire. Participants were informed about the purpose of the survey and asked to sign a consent form before the questionnaire was administered.

Estimation of underreporting and burden of syndromic and laboratory-confirmed AGE
Data on syndromic and laboratory-confirmed AGE reported to the Health Information Unit of the national surveillance were compared with data from the population and laboratory surveys (including the reporting and underreporting levels that occur in the country from the time when a person is ill with AGE/diarrhoeal disease to the time when it is documented in the national surveillance system).
Data from the surveys include information on seeking medical care, request for stool specimen, submission of stool specimen, and testing of stools. These are used in producing national estimates of the burden and extent of underreporting for syndromic AGE and laboratory-confirmed FBD/AGE pathogens, using the models shown in the burden of illness pyramid.

Estimation of economic and social impact
The economic burden of AGE was estimated using data from the population survey, e.g. percentage seeking medical care in public and private healthcare system, taking medication, type of meditation, hospitalization, adults losing median number of work days, and adults requiring caregiver for median number of days during his/her illness. The cost of medical supplies in public healthcare was obtained from the Central Medical Store whereas an average cost was used for private services and supplies from private clinics and dispensaries (7).

Response rate and representativeness of respondents
Of the total residents in 1,210 randomly-selected households, 973 individuals were contacted-478 in Phase 1 and 495 in Phase 2-with an overall response rate of 80.4%. Comparison of the demographic profile of Dominican residents (general population) and the survey respondents indicates that, overall, respondents were older than the census population and were more likely to be female ( Table 1).

Magnitude of illness
Of the 973 respondents, 91 (9.4%) reported that they had sudden onset of diarrhoea (3 or more watery or loose stools within 24 hours with or without fever, vomiting, or visible blood in the stool) in the 4 weeks prior to the interview and were, therefore, classified as self-reported cases of acute gastroenteritis (AGE). Of these 91 cases, 7 (7.7%) stated their symptoms were due to pre-existing/chronic conditions. Since the objective of the study was to describe AGE illnesses, these 7 respondents were included in the non-case group. Of the 84 remaining cases of AGE, 20 (23.8%) reported more than one episode in the 28 days prior to the interview. The period prevalence of self-reported AGE was 8.6% (95% CI 7.0-10.6). The yearly incidence rate was 1.1 episodes per person-year ( Table 2). The monthly prevalence for the high-and low-AGE seasons observed previously was not significantly different (low-AGE season 9.2%, 95% CI 6.8-12.2; high-AGE season 8.0%, 95% CI 5.9-10.9).

Distribution of illness
The monthly prevalence of AGE by age-group, gender, education of male and female household heads, ethnic group, and monthly household income are outlined in Table 1. Using univariate analysis, the monthly prevalence of AGE was found higher among females (10.8%) than males (6.7%). This difference was statistically significant (p=0.04).
The highest monthly prevalence of AGE was among the 1-4 year(s) age-group (25.0%), followed by 15-24 years (10.6%), 5-14 years (10.4%), and over 65 years age-group (9.5%) ( Figure 1). These differences were not statistically significant (p=0.14). The age-and gender-adjusted monthly prevalence of AGE were 9.9% and 8.4% respectively. There was no significant difference between the crude and age-adjusted monthly prevalence of AGE and gender-adjusted monthly prevalence of AGE.
Prevalence of AGE also varied by health district, with the highest monthly prevalence of self-reported cases of AGE being reported in the Portsmouth district (13.1%), followed by St. Joseph (12.6%) and Roseau district (9.3%) and the lowest reported in Grand Bay (2.1%) ( Figure 2). This difference across the health regions was statistically significant (p=0.01).

Symptoms and severity
In the 84 cases, the most common secondary symptoms included nausea (28.6%), followed by headache (25.0%), cough (25.0%), runny nose (20.2%), sneezing (17.9%), and vomiting (14.3%) ( Table 3). The maximum number of stools per 24 hours ranged from 3 to 9, with a median of 4. The average number of days an individual suffered from AGE was 2.5, with a range of 1-28 day(s) and a median of 2 days (Table 2). Of the 84 cases, 42 reported restricted activity and had to spend time at home due to their illness. The range of days spent at home was 1-7, with a me-    (Table 3). Fourteen cases required other individuals to look after them while ill. The range of days taking care of a case was 1-28, with a median of 2 days.

Healthcare-seeking behaviours
Of the 84 cases, 14 (16.7%) sought medical care for their illness. Six attended an outpatient clinic in a public hospital, 6 attended a health centre, and 2 went to a private physician. No cases reported having been hospitalized. Five cases had a stool specimen requested for (Table 4). Eight out of 14 cases who sought medical care reported having medication prescribed. Three were prescribed antibiotics, two of whom completed the course of antibiotics and one of whom did not, for an unknown reason. Four individuals were prescribed oral rehydration solution. Three were prescribed vitamins and antihelminthic medication. Thirtyseven cases took non-prescribed medications for their illnesses. Of them, 24 took 'unknown bush medicine'.

Risk factors, habits, and hygiene
Individuals were asked to identify what they believed to have caused their illness. Twenty-five (29.8%) cases believed they became ill from food consumption; 19 (22.6%) believed that water was the cause; and 5 (6.0%) believed contact with another sick person caused the disease. The number of individuals living in the households of respondents ranged from 1 to 13, with a median of 3. Households of non-cases and cases had a median of 3. This difference was not significant. Additionally, 19 cases reported that another individual was ill with diarrhoea in their home at the same time of their illness. Three reported 2 additional individuals to be ill, and four reported 3 others to be ill. Less than 10% of respondents reported washing their hands with or without soap before meals and after going to the toilet. However, handwashing was not significantly associated with being a case of AGE ( Table 5).
Out of 973 respondents, 9 went for swimming in the ocean, 7 went for swimming in the river, and 4 for swimming in the pool in the month prior to the interview. Swimming in the ocean, river or pool was not significantly associated with AGE (p=0.86, 0.98,

Laboratory survey
During April 2009 to March 2010, 73 diarrhoeal/ AGE stool samples were tested, and 47% were positive for an FBD pathogen-29% were positive for norovirus, 7% for Salmonella, 12% for Giardia, and 4% for Shigella. The laboratory practices and data are outlined in Table 7 and 8.

Estimating the underreporting and burden of AGE in Dominica
The distribution of the proportions of cases re-ported at each step in the reporting chain for AGE is outlined in Table 9. This input distribution was determined using syndromic and laboratoryconfirmed AGE data reported to the HIU, Ministry of Health and data from the population and laboratory surveys. Based on syndromic AGE data, the estimated burden of AGE for one year period (April 2009-March 2010) in Dominica was 6,720. The number of syndromic AGE cases reported to the Ministry of Health for the specified period was 1,120. Thus, there was an underreporting factor of 6 (6,720/1,120), (Figure 3). The overall underreporting rate for AGE in Dominica is 6 for every 1 reported case of AGE to the Ministry of Health. Using laboratory surveillance data, the estimated burden of laboratory-confirmed AGE for the one year period (April 2009-March 2010) in Dominica was found to be 3,080. The number of cases reported to Health Information Unit for the specified period  -10  8  8  6  ---6  -Mar-10  3  3  1  1  1  ---Total  73  73  34  11  5  3  21  9  Percentage  -100  47  32  7  4  29  12 was 11. There is an underreporting factor of 280 (3,080/11) for laboratory-confirmed foodborne/ AGE pathogens in Dominica ( Figure 4). The overall underreporting rate for laboratory-confirmed FBD/AGE pathogens in Dominica is 280 for every 1 case reported to the Ministry of Health.

Estimating economic burden of AGE
There are direct and indirect costs as a consequence of AGE. We were only able to estimate the direct cost due to the limited data available for calculating indirect cost in public health system (e.g. daily ser-vices of doctors, nurses, and others). The economic burden of AGE was estimated using cost data from both public and private healthcare systems.  (Table 12) .   *There was no data to differentiate between the percentages of those who purchased their medical supplies in public healthcare system and those in private healthcare system. Taking into consideration that those who sought medical care in private clinics (2.2%) also sought care from public health system, the cost of medical supplies was calculated using cost from the public health system only; **There were no cases of hospitalization; hence, it is unlikely to have had IV fluid, and hospitalization cost is not included in the estimation; ***As the distribution of loss of working days was skewed, median value was used rather than mean; ****20-64 years age-group was considered 'working group'. There was no data on occupation

DISCUSSION
The purpose of this study was to estimate the burden and demographic distribution of acute gastroenteritis (AGE) in Dominica. It was the first study of its kind in Dominica. is detected by the current syndromic and laboratory-based surveillance systems for AGE, implying gaps in these systems. Many more cases of AGE are occurring in the population of Dominica than are reported, and much more money is being spent on AGE-related illness than is being reported. These results should, therefore, be used in advocating for resources to improve AGE and to design appropriate interventions to reduce the burden of AGE in Dominica.
The prevalence of AGE in our study (8.6%) was lower than the prevalence of AGE in Cuba and other developed countries (8)(9)(10)(11). The yearly incidence rate was 1.1 episodes per person-year. When Although the seasonal difference in prevalence (9.2% in low and 8.0% in high season) was contrary to the data available at the surveillance unit, there was very little variance in AGE surveillance data throughout the study period. Furthermore, public announcements for proper handwashing and hygiene practice during pandemic H1N1 outbreak in Dominica may have impacted these results.
In this study, females were 1.6 times more likely to experience acute diarrhoeal disease than males. This is consistent with other studies (10,(13)(14)(15)(16) where higher rates were observed in females than males. The reasons for this may be due to differences in route of exposure, such as food preparation (17), or differences in biology. Nonetheless, in-depth studies of the specific reasons for such an increase are needed to implement appropriate prevention measures aimed at decreasing burden of disease in this sub-population.
The highest monthly prevalence of AGE was among the 1-4 year(s) age-group (25.0%), followed by 15-24 years (10.6%) and 5-14 years age-group (10.4%), which is consistent with international findings (9,11,13). Younger children are at a higher risk for AGE due to poor hygienic practices, resulting in ingestion of contaminated food and water (18,19). Overall, the rate of handwashing before meals and after using the toilet, particularly with soap, was not high; this may have contributed to the spread of disease. Although the association between agegroup and illness was insignificant (p=0.14), the prevalence of AGE was higher among the under-5 children; similar results of increased risk in children were found in many other studies (10,12). The lack of association may be due to sample-size rather than true lack of association in the population. Only 16.7% of cases sought medical care despite free healthcare services and supplies within the primary healthcare system, which is significantly lower compared to the study conducted in Cuba (9). The reason for not seeking care may be that the duration of illness was not long enough (median 2 days) to warrant a visit, and/or the illness was not severe enough, which seems to be suggested by the fact that there were no hospitalizations among the respondents. Only 35.7% of those who sought medical care were asked to submit stool samples, and 40% submitted samples. A substantial proportion of cases (44%) who did not seek healthcare treated the symptoms with homemade (bush/herbal) remedies. This indicates that there is still a substantial burden and additional cost associated with cases who do not seek formal medical care.
The predominant pathogen isolated over the study period was norovirus, followed by Giardia, Salmonella, and Shigella. This was markedly different from the laboratory-based AGE data reported to the national surveillance system, which showed that Salmonella was the most common pathogen. This finding has significant implications for our surveillance and intervention measures. Unlike Salmonella, norovirus is a highly-contagious viral pathogen. Transmission can occur through many routes, including faecal-oral, person-to-person, by aerosolized faecal material or vomitus and from touching contaminated surfaces. Infected persons continue to shed the pathogen after the symptoms have subsided, and shedding can still be de-tected many weeks after infection (20). To prevent and control norovirus outbreaks, pathogen-specific prevention guidelines need to be adopted in Dominica.

Limitations
Several limitations affected this study. Selection bias was evident since the age and gender distributions of the study participants differed from those of the census population (2009 mid-year estimate). Similar to other studies, another potential limitation of this study is recall bias due to reliance on the respondents' recollection of events over the previous four weeks.

Conclusions
For the first time in Dominica, this study provides evidence of a significant health burden and distribution of diarrhoeal disease. Overall, 1.1 episodes occur per person-year, with higher rates in females and those aged <5 years in Dominica. These highrisk groups should be considered when allocating resources. The estimated burden of AGE and AGE pathogens is substantially higher than that reported to the Ministry of Health, highlighting the fact that these enteric pathogens still pose a significant health burden. It is essential to design appropriate interventions and to minimize the impact of these pathogens in the population. The findings of this study will be applied to advocate for improved reporting of foodborne pathogens to the Ministry of Health.